The present invention relates to the field of turbomachine blades or vanes, and in particular the field of turbomachine rotor blades.
The term “turbomachine” is used in the present context to designate any machine in which energy can be transferred between a fluid flow and at least one set of blades, such as for example: a compressor, a pump, a turbine, or indeed a combination of at least two of these. In the description below, the terms “upstream” and “downstream” are defined relative to the normal flow direction of the fluid through the turbomachine.
Such a turbomachine may comprise a plurality of stages, each stage normally comprising two sets of blades and vanes, specifically a set of moving blades and a set of guide vanes. Each set of blades or vanes comprises a plurality of blades or vanes that are offset from one another in a lateral direction. Typically, such blades or vanes are arranged radially around a central axis A. Thus, such a set forms a rotor, when it is a set of moving blades, or a stator when it is a set of guide vanes. The proximal end of each blade or vane relative to the central axis A is normally referred to as its root, while the distal end is normally referred to as its tip. The distance between the root and the tip is referred to as the “height”. Between its root and its tip, a blade or vane is made up of a stack of aerodynamic profiles that are substantially perpendicular to a radial axis Z. The term “substantially perpendicular” is used in this context to mean that the plane of each profile may present an angle close to 90°, e.g. lying in the range 60° to 120°, relative to the radial axis Z.
The geometrical shape of blades is the subject of major design efforts in order to optimize the aerodynamic behavior of blades, thereby increasing the efficiency of the rotary assemblies such as compressors, fans, or turbines, of which they form a part. Thus, aerodynamic engineers propose relationships for stacking aerodynamic profiles that are optimized from the aerodynamic point of view.
Nevertheless, such stacking relationships are not necessarily optimized, nor even acceptable, from a mechanical point of view. For example, stacking relationships that are particularly effective from an aerodynamic point of view have been proposed in which a major portion of the blade is cantilevered out relative to the remainder of the blade. Such a large cantilevered-out mass is then highly sensitive to centrifugal forces resulting from the rotation of the rotor and leads to significant bending of the high portion of the airfoil, thereby leading to large mechanical stresses in the middle of the airfoil with static stresses that are too high at the “red line” flight point, i.e. the emergency flight point. Under such circumstances, such blades have only a very small dynamic margin and, in the event of an impact or in the event of the rotary assembly surging, they withstand fatigue poorly.
Conversely, other stacking relationships that are optimized from a mechanical point of view have been proposed by mechanical engineers, but they have not been accepted because of their aerodynamic performance being insufficient.
There therefore exists a real need for a blade that benefits both from good aerodynamic properties and from good mechanical properties.